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This is for a DIY project I'm working on. I know I could just monitor the charging process and unplug before the capacitor blows, or get a more suitable power supply, but it just so happens that I have a bunch of capacitors rated at 1000 V and a transformer that gives me 6000 V DC. I'd like to use this rather than spend extra on getting another transformer.

Let's say I put the capacitor in parallel with a resistor, and this in series with another resistor, i.e. I'm using a potential divider to limit the capacitor output, like this:

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Initially, the capacitor is going to be like a short circuit, so it'll charger very rapidly, but as it fills up, more charge will go through R1 instead. When the capacitor is charged at $V = V_{in} \times R_1 / (R_1+R_2)$, there should be no current passing through the capacitor.

This seems like a very simple situation to me, but for some reason I don't see anyone doing this or any information about a circuit like this online (or maybe I'm just not using the right search terms...)

Am I missing out something fatal that'll completely screw up my capacitors if I try this?

Also, any tips on choice of resistor size? I'd probably want to use the most resistant resistors I have to keep current flow small.

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So to get 1000V from the 6000V supply you need a ratio of 1:5

higher resistance will cause slower charging.

Pick a resistance that would give an acceptable result if used with a 1000V supply, then choose your R1,R2 such that their parallel combination is that resistance. and their ratio is 1:5.

can you instead use a step-down tranformer on the input to the 6000V supply?

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  • $\begingroup$ Just to clarify, when you say "pick a resistance that would give an acceptable result if used with a 1000 V supply", you mean adding a resistance in series with the capacitor to slow down the current to the capacitor, right? As for the step down transformer, I don't have one at the moment, just avoiding having to spend on additional stuff for a one-time-off project. $\endgroup$
    – Nic
    Commented Jan 8, 2017 at 8:08
  • $\begingroup$ yes, I mean in series with the 1000V supply, between it and the capacitor. The transformer would only need to be about 1/36 the size of the one in the 6000V supply $\endgroup$
    – Jasen
    Commented Jan 8, 2017 at 8:29

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